This invention relates to an apparatus for controlling rotation of a spindle motor in a disk player such as a video disk player, etc.
As a video disk on which information in a video format is recorded, there exist a CAV (Constant Angular Velocity) disk on which information is recorded at a constant angular velocity and a CLV (Constant Linear Velocity) disk on which information is recorded at a constant linear velocity.
In a CAV disk, it is required to fix the number of rotations of the motor to be a predetermined angular velocity (e.g., 1800 rpm). Further, in a CLV disk, it is required to change the rotation velocity of the disk in dependency upon the information reading position in a radial direction of the disk.
To realize this, in both the CAV disk and the CLV disk, a spindle servo loop for carrying out a control in which the rotation velocity is kept to be constant and a time base servo loop for carrying out a fine adjustment of a reproduced signal with respect to the time base are necessarily required.
By the action of these servo loops, the rotation velocity of the CLV disk can be controlled to be a constant linear velocity. When a CLV disk is reproduced, in the case where the servo loops are forcedly opened, or the servo loops undesirably deviate from followable range by disturbance from outside, so the rotation velocity of the spindle motor greatly deviates from a normal rotation velocity, it is necessary to quickly restore the rotation velocity of the spindle motor to be within the followable range of the spindle servo loop.
In a conventional apparatus, in the case where the servo loops undesirably deviate from an allowable followable range, returning operation to the lock state was conducted as follows.
Between the rotation velocity of the spindle motor and the level of a read RF signal at that rotation velocity (i.e., DC (Direct Current voltage) level of a reproduced video signal), there exists a fixed correlation. Namely, when the rotation velocity of the spindle motor is high, the DC level of the video signal is high, while when the rotation velocity of the spindle motor is low, the DC level of the video signal is low. In view of this, a procedure is first taken to detect the DC level of the video signal by using a window comparator, whereby when the DC level deviates from a predetermined followable range (e.g., the range expressed as V1&gt;V&gt;V2) of the spindle servo loop, the spindle servo loop is opened.
Then, the spindle motor is accelerated or decelerated until the rotation velocity becomes within the followable range of the spindle servo loop. After the rotation velocity of the spindle motor becomes within the followable range of the spindle servo loop, the spindle servo loop is closed. Thus, the spindle motor is returned to a lock state by the followable action of the spindle servo loop.
The outline of such a prior art is described in the U.S. Pat. No. 5,051,976.
It is generally said that the range where the spindle servo loop can be pulled in is approximately .+-.15% with respect to a normal rotation velocity. Accordingly it is requried to set the voltages V1 and V2 serving as a reference voltage of the window comparator to voltages of approximately .+-.15% with respect to the DC level of a video signal obtained at the time of a normal rotation velocity.
However, setting the reference voltages V1 and V2 in every products results in an increase of the manufacturing cost, and two reference voltage setting volumes, etc. are required.